Filariasis comprises a collection of vector-borne worm diseases affecting humans throughout the tropical regions of the world. Worldwide 905 million people are at risk from lymphatic filariasis--caused mainly by Wuchereria bancrofti or Brugia malayi--90 million of whom are infected; serious cases have to live with the gross deformations of elephantiasis. Similarly 90 million people are at risk from onchocerciasis, 17.6 million of whom are actually infected; of these some 326,000 have lost their sight due to the activities of the microfilariae in the eye.
Drug treatment of filariasis has been unsatisfactory. Diethylcarbamazine has the ability to destroy microfilariae, but unpleasant and sometimes dangerous allergic side effects may occur; it also has the ability in adequate doses to kill adults of lymphatic filariae in some, but far from all patients. Suramin and derivatives of melaminylarsonic acid also have macrofilaricidal action. However, their toxicity, and the fact that they have to be given repeatedly and by injection, make them unsatisfactory candidates for mass treatment. Benzimidazoles, such as flubendazole and mebendazole, are widely used for the treatment of intestinal helminth infections in mammals, but they are poorly absorbed and cause pain and inflammation on injection. Thus, none appears suitable for the mass treatment of filariasis infections. More recently it has been found that ivermectin has outstanding activity against microfilariae, but is without effect on adult worms. Treatment once or twice a year with ivermectin combined with a vector control programme forms the basis of the Onchocerciasis Control Programme in West Africa. While regular control of microfilariae with ivermectin will prevent the development of blindness in onchocerciasis, killing of adult worms would give better control of onchocerciasis, and is essential to prevent the development of pathology in lymphatic filiariasis. Therefore, the development of new soluble macrofilaricides which are well absorbed by oral administration and are not irritating upon parental administration is essential for the global management of filariasis.